Light-emitting diodes (hereinafter referred to as “LEDs”) and laser diodes are known as light-emitting devices including semiconductors. For example, an LED including a Group III-V compound semiconductor is produced through epitaxial growth of a layer of GaP, GaAsP, GaAs, GaAlAs, GaAlInP, or GaN on a single-crystal substrate of GaP or GaAs. The LED includes pn-junction portions which are formed of one or more p-type layers and one or more n-type layers, and has an appropriate structure such that light is emitted when electrons are introduced into the pn-junction portions.
In an LED, light is emitted from a pn-junction portion in all directions. In contrast, a laser diode exhibits high emission directivity, and thus is used when light is required to be emitted in a specific direction. However, a laser diode involves disadvantages, in that it is expensive and requires high power for operation thereof, and thus LEDs exhibiting emission directivity have been proposed. For example, there has been proposed a current-constricting LED, which is formed by partial modification of a conventional LED and exhibits enhanced emission directivity. However, a current-constricting LED involves disadvantages, including difficulty in control of epitaxial growth of crystal and low reliability attributed to flow of high current to a portion of the crystal. In addition, although a current-constricting LED is less expensive than a laser diode, the LED has a complicated structure and is expensive as compared with a conventional LED.
In order to enhance emission directivity of a conventional LED, a reflection plate or a reflection cup is provided or formed on the frame of a light extraction section of the LED. However, when a reflection plate or a reflection cup is provided or formed, the resultant light-emitting apparatus may be expensive, and miniaturization of the apparatus is difficult, which is unsatisfactory. In addition, a light emission region cannot be formed as small as that of a laser diode or a current-constricting LED, and thus such a conventional LED is difficult to use as a point-source light.
In order to use such a conventional LED as a point-source light, there is proposed an LED including a window for light extraction on the upper electrode. However, light which leaks from the side of the LED becomes stray light, and thus noise increases and S/N ratio decreases. As a result, emission directivity of the LED is similar to that of a conventional LED.